We investigate a stochastic model describing a column of grains in the
jamming limit, in the presence of a low vibrational intensity. The key control
parameter of the model, ϵ, is a representation of granular shape,
related to the reduced void space. Regularity and irregularity in grain shapes,
respectively corresponding to rational and irrational values of ϵ, are
shown to be centrally important in determining the statics and dynamics of the
compaction process.Comment: 29 pages, 14 figures, 1 table. Various minor changes and updates. To
appear in EPJ